JP2007336681A - Drive unit for piezoactuator and its drive method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a drive unit for piezoelectric actuator which can be driven for a long time in a stable state. <P>SOLUTION: This drive unit for a piezoelectric actuator is a drive unit 1 for a piezoelectric motor. It includes a memory 14 wherein resonance frequency f1 with which an electrostrictive revolver 11 starts its drive is to be stored, a current detector 12 which detects the current flowing to the electrostrictive revolver 11, and a controller 13 which controls the frequency of a drive signal inputted into the electrostrictive revolver 11. Then, the controller 13 controls the frequency f of the drive signal, according to the detected current detected by the current detector 12 in the frequency band of f1 or over in frequency with which the revolver has started the drive. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a driving device for a piezoelectric actuator and a driving method thereof.

  2. Description of the Related Art In recent years, a piezo motor (electrostrictive rotator type motor) using an electrostrictive rotator composed of piezo elements has been developed. The piezo motor generates a revolution torque by inputting a four-phase pulse signal having a resonance frequency of a piezo element to an electrostrictive revolution element mounted thereon, and rotates a rotor pressed against the electrostrictive revolution element. The piezo motor has a simple structure and can be reduced in size and thickness, and has advantages such as low speed, high torque, and high resolution.

  In order to stably rotate such a piezo motor, it is necessary to input a drive signal whose frequency is the resonance frequency of the piezo element. When driving a piezo motor by inputting a drive signal to the piezo element, the behavior of the piezo motor differs depending on whether the frequency is raised from a low value or lowered from a high value. 5 and 6 show the operating characteristics (frequency / signal current characteristics) of the piezoelectric motor.

  As shown in FIG. 5, when the frequency is increased from a low value, the motor remains stopped at a value lower than the resonance frequency (recovery frequency), and when the return frequency is passed, the motor rotates to stop the rotation. When it reaches, the rotation stops. On the other hand, when the frequency is lowered from a high value, it stops at the step-out frequency without stopping even if it passes through the return frequency.

  Therefore, the resonance frequency and current of the piezo element are measured in advance, and an appropriate drive signal is input to the piezo element based on the data. As shown in FIG. 6, in the operating characteristics of the piezo motor, the resonance frequency f0 is shifted to the frequencies f1 and f2 due to various factors such as heat generated while the motor is driven. For this reason, since the value of the current flowing through the piezoelectric element at a predetermined frequency changes, it is difficult to maintain a steady state even when a drive signal having a constant frequency is always input. In order to cope with this, there is a method of feeding back the drive current from the piezo motor, controlling the frequency of the drive signal to be appropriate, and maintaining the maximum current (peak current) (see, for example, Patent Document 1).

Further, even if feedback control of the frequency of the drive signal is performed, the piezo motor has a nonlinear characteristic, so that there is a risk that the rotation will stop due to reaching the step-out frequency. Therefore, it is possible to drive the piezo motor while maintaining a stable state to some extent, but it is difficult to drive the piezo motor while maintaining a stable state for a long time. Furthermore, since the resonance frequency is slightly different for each piezo element, it is difficult to set a common resonance frequency for stably operating many piezo elements. Furthermore, since the electrostrictive revolution rotator has hysteresis characteristics, the resonance frequency changes even with the same piezo element.
JP 2002-359988 A

  As described above, the conventional method for driving a piezo motor has a problem that it is difficult to drive in a stable state for a long time due to the nonlinear characteristics of the piezo motor and the hysteresis characteristics of the electrostrictive revolution rotator.

  The present invention has been made to solve such problems, and an object of the present invention is to provide a driving device for a piezoelectric actuator that can be driven in a stable state for a long time and a driving method thereof.

  A drive device for a piezo actuator according to the present invention is composed of a piezo element, and an electrostrictive revolution element that generates a drive force in response to a drive signal composed of continuous pulses, and a movable that converts the drive force into an actual motion. A device for driving a piezo actuator having a child, a storage unit storing a drive start frequency at which the electrostrictive revolution element starts driving, and current detection for detecting a current flowing through the electrostrictive revolution element And a control unit that controls the frequency of the drive signal input to the electrostrictive revolution rotator, and the control unit detects the detected current detected by the current detection unit in a frequency band equal to or higher than the drive start frequency. Accordingly, the frequency of the drive signal is controlled. In such a configuration, the electrostrictive rotator can be driven by a drive signal having a drive start frequency that allows a peak current to flow. Can be time driven.

  Further, the control unit increases the frequency of the drive signal input to the electrostrictive revolution rotator when the current value of the detection current increases, and when the current value of the detection current decreases, Reduce the frequency of the drive signal input to the electrostrictive revolution.

  Further, the control unit inputs a drive signal to the electrostrictive rotator while increasing the frequency of the drive signal as power is turned on to the piezo actuator, and the electrostrictive rotator starts driving. The drive start frequency is stored in the storage unit.

  The piezo actuator according to the present invention is driven by such a driving device. In such a configuration, the electrostrictive rotator can be driven by a drive signal having a drive start frequency that allows a peak current to flow. Can be time driven.

  A driving method of a piezo actuator according to the present invention is composed of a piezo element, and an electrostrictive revolution rotator that generates a driving force according to a driving signal composed of continuous pulses, and a movable that converts the driving force into an actual motion. A method for driving a piezoelectric actuator having a child, the step of storing a driving start frequency at which the electrostrictive revolution element starts driving, the step of detecting a current flowing through the electrostrictive revolution element, and the driving And a step of controlling the frequency of the drive signal in accordance with a detected current detected by the current detector in a frequency band equal to or higher than a start frequency. In such a configuration, the electrostrictive rotator can be driven by a drive signal having a drive start frequency that allows a peak current to flow. Can be time driven.

  Further, in the step of controlling the frequency of the drive signal, when the current value of the detected current increases, the frequency of the drive signal input to the electrostrictive revolution rotator is increased and the current value of the detected current decreases. If this happens, the frequency of the drive signal input to the electrostrictive rotator is lowered.

  Further, the driving method of the piezo actuator according to the present invention includes a step of turning on the power to the piezo actuator, and a step of inputting a driving signal to the electrostrictive revolution rotator while increasing the frequency of the driving signal according to the turning on of the power. And a step of storing the driving start frequency at which the electrostrictive revolution element starts driving. As a result, the electrostrictive rotator constituted by the piezo elements can be driven at the drive start frequency according to the initial state when the power is turned on.

  ADVANTAGE OF THE INVENTION According to this invention, the drive device of the piezo actuator which can be driven for a long time in a stable state, and its drive method can be provided.

  The piezo actuator driving apparatus according to the present invention drives the piezo actuator while holding the electrostrictive rotator so that the drive current of the electrostrictive rotator becomes maximum in a frequency range higher than a resonance frequency (demodulation frequency) at which driving is started. is there. Specifically, this drive device gradually increases the frequency of the drive signal to the demodulation frequency to start driving the piezoelectric actuator, and drives the piezoelectric actuator in a frequency range higher than the demodulation frequency.

  Hereinafter, the best mode for carrying out the present invention will be described with reference to the drawings. In the present embodiment, a piezo motor will be described as a suitable example of a piezo actuator. However, the present invention is not limited to this, and various actuators can be configured by variously changing a driving force transmission mechanism.

  First, the configuration of a piezo motor driving apparatus according to the present invention will be described with reference to FIG. FIG. 1 is a block diagram showing a configuration example of a driving device for a piezo motor according to the present invention.

  As shown in FIG. 1, a piezo motor driving apparatus 1 according to the present invention includes a driving mechanism 10, an electrostrictive revolution rotator 11, a current detection unit 12, a control unit 13, a storage unit 14, a voltage control oscillator 15 (hereinafter referred to as a VCO 15). Abbreviated).

  The drive mechanism 10 is a drive mechanism that drives a piezo motor, and details thereof will be described later. The electrostrictive revolution element 11 is constituted by a so-called piezo element that expands and contracts in accordance with an input drive signal, and generates a driving force of the piezo motor. The current detection unit 12 includes an ammeter or the like, and detects a current flowing through the electrostrictive revolution rotator 11 being driven. The control unit 13 includes a CPU, an MPU, and the like, and performs operation control of the drive device 1.

  The storage unit 14 includes a ROM, a RAM, a hard disk drive, and the like, and stores programs and data necessary for various processes for driving the piezo motor. The storage unit 14 stores a demodulation frequency of a drive signal for driving the electrostrictive revolution rotator 11. The recording unit 14 further stores, for example, data such as the current value of the current flowing through the electrostrictive revolution rotator 11, and a control program for controlling the drive signal using the frequency and current value of the drive signal. ing. The VCO 15 is an example of a drive signal generation unit that generates a drive signal for driving the electrostrictive revolution rotator 11, and outputs a drive signal by changing the frequency of the drive signal in accordance with the input voltage.

  In such a driving apparatus 1, when the drive mechanism 10 drives the electrostrictive revolution rotator 11, the current detection unit 13 detects a current flowing through the electrostriction revolution rotator 11. The current detection unit 13 inputs the detected current value of the detected current to the control unit 13, and the control unit 13 stores the input current value in the storage unit 14. The control unit 13 calculates a voltage value for controlling the VCO 15 from this current value, and inputs the voltage of this voltage value to the VCO 15. Here, the control unit 13 calculates a voltage value for controlling the VCO 15 based on the frequency of the drive signal input to the electrostrictive revolution rotator 11.

  The VCO 15 inputs a drive signal having a predetermined frequency to the electrostrictive revolution rotator 11 based on the input voltage, and drives the electrostriction revolution rotator 11. The drive device 1 feeds back the current flowing through the electrostrictive revolution rotator 11 until the electrostrictive revolution rotator 11 starts to be driven, and while the electrostrictive revolution rotator 11 is driven. The control of the child 11 is repeated. Although not shown, each of these functional units is driven when power is supplied from a power source unit for driving the piezo motor.

  Next, the drive mechanism 10 of the drive device 1 according to the present invention will be specifically described with reference to FIG. FIG. 2 is a schematic diagram showing a configuration example of the drive mechanism 10 of the drive device 1 according to the present invention.

  A structural example of the electrostrictive revolution rotator 11 is shown in the external view of FIG. As shown in FIG. 2A, the electrostrictive revolution rotator 11 has a substantially cylindrical shape, and grooves are formed in the longitudinal direction so as to be divided into four along the outer periphery thereof. The rotor 101 is pressed against the end surface of the substantially cylindrical electrostrictive revolution element 11, and the electrostrictive revolution element 11 functions as a stator with respect to the rotor 101.

  A configuration example of the electrostrictive revolution rotator 11 is shown in the plan view of FIG. As shown in FIG. 2B, each of the four divided parts of the electrostrictive revolution rotator 11 is electrically connected to the control unit 13 via the VCO 15. At this time, each of the four divided parts of the electrostrictive revolution rotator 11 is connected in parallel to the VCO 15, and an alternating signal in which the polarity of the drive signal is periodically switched is applied. That is, the control unit 13 also functions as a switching unit that switches and applies the drive signal to each of the four divided portions of the electrostrictive revolving rotator 11.

  An example of a drive signal input to the electrostrictive revolution rotator 11 is shown in the waveform diagram of FIG. As shown in FIG. 2 (c), each of the divided parts of the electrostrictive revolution rotator 11 includes, for example, four AC voltages having different phases (A phase voltage, B phase voltage, C phase voltage, D phase voltage). ) Is applied. The phase of the B phase voltage is shifted by 90 ° with respect to the phase of the A phase voltage. The phase of the C phase voltage is shifted by 180 ° with respect to the phase of the A phase voltage, and the phase of the D phase voltage is shifted by 270 ° with respect to the phase of the A phase voltage. That is, the phases of the A phase voltage, the B phase voltage, the C phase voltage, and the D phase voltage are sequentially shifted by 90 °.

  When four AC voltages having phases shifted in this order by 90 ° are applied to the electrostrictive revolution rotator 11, different revolution vibrations are generated in each of the four divided portions of the electrostrictive revolution rotator 11. Specifically, a pair of adjacent parts generate the same revolution vibration, and the revolution vibrations occur so that these one part part rotates. Since the rotor 101 is in pressure contact with the electrostrictive revolution element 11, the center of gravity of the rotor 101 resonates so as to rotate around the center of the end face of the electrostriction revolution element 11. Thereby, rotational torque is generated in the rotor 101 and revolves with respect to the electrostrictive revolution rotator 11 while being eccentric like a hula hoop. As described above, the electrostrictive revolution rotator 11 is excited in the resonance state by the control unit 13 switching the applied voltage to generate the revolution torque.

  Next, the operation process of the drive device 1 according to the present invention will be described with reference to FIG. FIG. 3 is a flowchart showing an example of operation processing of the drive device 1 according to the present invention. Here, it demonstrates, referring FIG. 4 suitably. FIG. 4 is a schematic diagram showing changes in operating characteristics of the piezo motor driven by the driving device 1.

  When the power is turned on in the initial stage, the control unit 13 controls the VCO 15 to input a drive signal having an initial frequency to the electrostrictive revolution rotator 11 (S101). At this time, the initial frequency is a frequency smaller than the resonance frequency of the piezoelectric element constituting the electrostrictive revolution rotator 11. The controller 13 causes the VCO 15 to input a drive signal having a predetermined frequency to the electrostrictive revolution rotator 11 while gradually increasing the frequency from the initial frequency (S102). Then, the control unit 13 instructs the electrostrictive revolution rotator 11 to rotate at the set frequency f (S103).

  The control unit 13 detects the driving of the electrostrictive rotator 11 based on the detection current detected by the current detection unit 12 (S104). Specifically, the control unit 13 determines that the electrostrictive revolution rotator 11 is not driven when the current value of the detection current input from the current detection unit 12 is approximately 0, and the current value of the detection current is When it is not substantially 0, it is determined that the electrostrictive revolution rotator 11 is driven.

  The control unit 13 inputs a drive signal to the electrostrictive revolution rotator 11 while increasing the frequency until the electrostrictive revolution rotator 11 starts to drive, and records the frequency of the drive signal at the time of starting the drive. Specifically, when it is determined that the electrostrictive revolution rotator 11 is not driven (S104), the control unit 13 increases the frequency of the drive signal until the electrostrictive revolution rotator 11 starts driving, and this drive signal Is input to the electrostrictive revolution rotator 11. When it is determined that the electrostrictive revolution rotator 11 is driven (S104), the control unit 13 further sets the current value detected by the current detection unit 12 as the frequency f1 of the drive signal input at that time. It preserve | saves at the memory | storage part 14 (S105, S106).

  The current detection unit 12 detects the current flowing through the electrostrictive revolution rotator 11 even after the electrostriction revolution rotator 11 starts driving, and inputs the current value of the detected current to the control unit 13. When the current value of the detected current is input from the current detection unit 12, the control unit 13 temporarily stores the current value of the detected current in the storage unit 14 (S107). When the detection current is further input from the current detection unit 12, the control unit 13 compares the current value of the current detection current with the current value at the previous detection previously stored in the storage unit 14 (S <b> 108 and S <b> 111). . When the current value of the current detected current is equal to the current value at the previous detection previously stored in the storage unit 14 (S108), the control unit 13 maintains the drive frequency f (S109). And the control part 13 instruct | indicates the rotational drive with the setting frequency f to the electrostriction revolution rotator 12 (S110), and returns to step S107 in which the electric current detection part 12 detects the electric current which flows into the electrostriction revolution rotator 11. FIG.

  When the current value of the detected current detected at that time is larger than the previously detected current value stored (S108, S111), the control unit 13 sets the drive signal set frequency f by a predetermined amount, for example, about 250 Hz. (S112). As shown in FIG. 4A, when the current value of the detected current is larger than the stored current value, the operating characteristics of the piezo motor are shifted in the direction of increasing the frequency. Therefore, the resonance frequency of the electrostrictive revolution rotator 11 is higher than the resonance frequency f1 stored in advance due to various factors such as heat generated during driving. Therefore, since the frequency f of the drive signal that the electrostrictive revolution rotator 11 is actually driving approaches the step-out frequency, the frequency f of the input drive signal is increased. Thereafter, the control unit 13 instructs the electrostrictive rotator 12 to rotate at the set frequency f (S110), and the current detection unit 12 returns to step S107 where the current flowing through the electrostrictive rotator 11 is detected.

  When the current value of the detected current is smaller than the stored current value (S108, S111), the control unit 13 decreases the frequency f of the drive signal by a predetermined amount (S113). The controller 13 compares the lowered drive signal frequency with the resonance frequency f1 (S114). When the frequency f of the driving signal at that time is higher than the resonance frequency f1 (S114), the control unit 13 instructs the VCO 15 to perform rotational driving at the set frequency f (S110), and the current detection unit 12 performs electrostriction. It returns to step S107 which detects the electric current which flows through the revolution element 11.

  When the frequency f of the lowered drive signal is equal to or lower than the resonance frequency f1 stored in the storage unit 14 (S114), the control unit 13 sets the frequency f of the drive signal for driving the electrostrictive revolving rotator 11 to the resonance frequency f1. (S115). Thereafter, the control unit 13 instructs the VCO 15 to rotate at the set frequency f (S110), and the process returns to step S107 in which the current detection unit 12 detects the current flowing through the electrostrictive revolution rotator 11.

  As shown in FIG. 4B, when the current value of the detected current is equal to or less than the stored current value, the operating characteristics of the piezo motor are shifted in the direction in which the frequency decreases. Therefore, the resonance frequency of the electrostrictive revolution rotator 11 is lower than the resonance frequency f1 stored in advance due to various factors such as heat generated during driving. Therefore, in order to increase the current value of the drive signal that drives the electrostrictive revolution rotator 11, the frequency f of the input drive signal is lowered. At this time, the frequency f of the drive signal may cause a step-out in order to lower the frequency f of the drive signal. However, in the present invention, since the frequency f of the drive signal is set to f1 or more, the frequency f of the drive signal is increased. The possibility of creating a tone is lost. Therefore, the electrostrictive revolution rotator 11 can be driven stably.

  As described above, in the driving device 1 according to the present invention, the peak value (maximum current value) of the current flowing through the electrostrictive rotator 11 during driving is increased by increasing the frequency of the driving signal from a low value when the initial power is turned on. The resonance frequency f1 corresponding to this is detected. Therefore, the electrostrictive revolution rotator 11 can maintain the state driven at the maximum current value in a frequency range higher than the resonance frequency f1. Therefore, it can be driven for a long time in a stable state without stepping out.

  In particular, since the frequency of the drive signal is increased when the current value of the detection current is increased, even if the resonance frequency of the electrostrictive revolution element is shifted in the increasing direction, step-out can be prevented. At the same time, when the current value of the detection current decreases, the frequency of the drive signal is lowered, so that even if the resonance frequency of the electrostrictive revolving rotator is shifted downward, it is possible to prevent reaching the stop point. it can. Accordingly, it is possible to reliably prevent any rotation stop point from being reached while using a frequency region higher than the resonance frequency.

  Further, when the initial power is turned on, driving of the electrostrictive rotator 11 is started while gradually increasing the frequency of the drive signal. Thereby, even if the state of the piezo element constituting the electrostrictive revolution rotator 11 is changed, it is possible to cope with the state, and the electrostriction revolution rotator 11 can be driven in an optimum state. In addition, by storing the resonance frequency of the electrostrictive revolution rotator 11 at the time of initial power-on, when the power is turned on for the second time, the operation can be performed by starting from the stored resonance frequency. As a result, it is possible to always start the motor promptly when the power is turned on.

It is a block diagram which shows one structural example of the drive device of the piezoelectric motor which concerns on this invention. It is a figure which shows an example of a structure of the electrostrictive revolution rotator which concerns on this invention. It is a flowchart which shows an example of the operation | movement process of the drive device of the piezoelectric motor which concerns on this invention. It is a graph which shows the operating characteristic of the piezoelectric motor which concerns on this invention. It is a graph which shows the operating characteristic of the conventional piezoelectric motor. It is a graph which shows the operating characteristic of the conventional piezoelectric motor.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 ... Piezo motor drive device, 10 ... Drive mechanism, 11 ... Electrostrictive revolution trochanter, 13 ... Control part,
14 ... storage unit, 15 ... voltage controlled oscillator (VCO)

Claims (7)

An electrostrictive revolution rotator that is composed of piezo elements and generates a driving force in response to a driving signal composed of continuous pulses;
A device for driving a piezo actuator having a mover that converts the driving force into actual motion,
A storage unit for storing a drive start frequency at which the electrostrictive revolution element starts driving;
A current detection unit for detecting a current flowing through the electrostrictive revolution rotator;
A control unit for controlling the frequency of the drive signal input to the electrostrictive revolution rotator,
The control unit is a drive device for a piezo actuator that controls the frequency of the drive signal in accordance with a detected current detected by the current detection unit in a frequency band equal to or higher than the drive start frequency. The controller is
When the current value of the detection current has increased, increase the frequency of the drive signal input to the electrostrictive revolution trochanter,
2. The drive device for a piezo actuator according to claim 1, wherein when the current value of the detection current decreases, the frequency of the drive signal input to the electrostrictive revolution rotator is lowered.   The control unit inputs a drive signal to the electrostrictive revolution rotator while increasing the frequency of the drive signal as power is turned on to the piezoelectric actuator, and the electrostriction revolution trochanter starts driving. The drive device for a piezo actuator according to claim 1 or 2, wherein a frequency is stored in the storage unit.   A piezo actuator driven by the drive device according to claim 1. An electrostrictive revolution rotator that is composed of piezo elements and generates a driving force in response to a driving signal composed of continuous pulses;
A method for driving a piezo actuator having a mover that converts the driving force into actual motion,
Storing a driving start frequency at which the electrostrictive rotator starts driving;
Detecting the current flowing through the electrostrictive revolution,
And a step of controlling the frequency of the drive signal in accordance with a detected current detected by the current detector in a frequency band equal to or higher than the drive start frequency. In the step of controlling the frequency of the drive signal,
When the current value of the detection current has increased, increase the frequency of the drive signal input to the electrostrictive revolution trochanter,
6. The method for driving a piezo actuator according to claim 5, wherein when the current value of the detected current decreases, the frequency of the drive signal input to the electrostrictive revolution rotator is lowered. Powering on the piezo actuator;
Inputting the drive signal to the electrostrictive trochanter while increasing the frequency of the drive signal according to the power-on;
The method of driving a piezo actuator according to claim 5, further comprising a step of storing the drive start frequency at which the electrostrictive revolution element starts driving.

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